Optical articles that provide good imaging qualities while reducing the transmission of incident light into the eye are needed for a variety of applications, such as sunglasses, vision correcting ophthalmic lenses, plano lenses and fashion lenses, e.g., non-prescription and prescription lenses, sport masks, face shields, goggles, visors camera lenses, windows, automotive windshields and aircraft and automotive transparencies, e.g., T-roofs, sidelights and backlights.
In response to certain wavelengths of electromagnetic radiation (or actinic radiation), photochromic materials undergo a transformation from one form or state to another form, with each form having a characteristic or distinguishable absorption spectrum associated therewith. Typically, upon exposure to actinic radiation, many photochromic materials are transformed from a closed-form, which corresponds to an unactivated (or bleached, e.g., substantially colorless) state of the photochromic material, to an open-form, which corresponds to an activated (or colored) state of the photochromic material. In the absence of exposure to actinic radiation, such photochromic materials are reversibly transformed from the activated (or colored) state, back to the unactivated (or bleached) state.
Photochromic plastic articles used for optical applications have been the subject of considerable attention. In particular, photochromic ophthalmic plastic lenses have been of interest because of the advantages associated with reduced weight that they can provide compared to glass lenses. Photochromic optical articles typically display colorless (e.g., clear) and colored states that correspond to the colorless and colored states of the photochromic materials contained therein. Photochromic compounds can be incorporated into optical articles, by methods including, imbibing a photochromic compound directly into an optical substrate, or by forming a photochromic coating layer over an optical substrate, which contains a photochromic compound.
Photochromic articles that include a photochromic coating layer further include, in some instances, a further layer, such as a protective layer, thereover. The protective layer can serve to protect the underlying photochromic layer from subsequently applied additional layers there-above. The protective layer is often formed from a protective layer coating composition. So as to form a continuous protective layer having a uniform thickness, the viscosity of the protective layer coating composition must typically be low. To reduce the viscosity of the protective layer coating composition to a desirable level, solvent is typically included in the protective layer coating composition. The amount of solvent present in the protective layer coating composition can have associated therewith concerns relating to increased economic costs and/or undesirable environmental impact.